Evaluation of commercial antisera for Shigella serogrouping

Abstract

Shigella serogrouping antisera from six companies (Becton Dickinson, Denka, Difco, Murex, Roach, and Sanofi-Pasteur) intended for the slide agglutination test and those of the Wellcolex Colour Shigella latex agglutination test were evaluated to identify quality products for Shigella identification. Forty-six reference Shigella strains (one for each serotype and species), 50 clinical strains (21 S. flexneri, 21 S. sonnei, 4 S. dysenteriae, 4 S. boydii) representing the most prevalent species and serotypes encountered in Quebec, and 9 non-Shigella strains were tested according to the manufacturers' instructions. A 3؉ reaction (>75% agglutination) was considered positive for the slide agglutination tests. Sensitivity varied from 47% (Roach) to 94% (Difco). For the 105 strains tested, accuracy ranged from 53% (Roach) to 91% (Wellcolex). Specificity varied from 97 to 100% for group A antisera, from 96 to 100% for group B antisera, from 88 to 100% for group C antisera, and from 95 to 99% for group D antisera. The costs of reagents required to test one strain varied from $3.50 to $13.20 (in Canadian dollars). In conclusion, Roach reagents proved to be unsatisfactory for Shigella serogrouping. Among those from the remaining companies, the Denka, Difco, and Wellcolex reagents met a performance standard of 90% accuracy. Shigella species are primarily responsible for gastrointestinal tract infections ranging from bacillary dysentery to less acute infections and are spread worldwide (1, 9-11, 13, 14). They share common characteristics with members of the genus Escherichia, from which they cannot be differentiated by DNA-DNA hybridization. According to modern taxonomy, subdivision of the genus into species is irrelevant. Nonetheless, medical and epidemiological interests justify maintaining the genus with its four species: S. dysenteriae, S. flexneri, S. boydii, and S. sonnei, also known as groups A, B, C, and D, respectively. These are subdivided into serotypes, which are given numerical designations (5-7, 13). Laboratory diagnosis relies on the isolation of the organism from feces and its identification by means of cultural and biochemical characteristics. Serological identification is mandatory because of its close relatedness to Escherichia coli. It requires, for a start, that species be identified (serogrouping); this is followed by serotype determination (serotyping). Serogrouping is generally carried out in clinical laboratories, while serotyping is performed in central or reference laboratories (5, 6, 13). Serogrouping is based on the detection of somatic O antigens by an agglutination technique with polyclonal antisera specific to each of the four Shigella species. Unfortunately, there is no international consensus on the choice of Shigella strains for the production of the grouping antisera (6). These antisera are commercially available from various manufacturers, but the sensitivities and specificities of these products remain to be determined. A study conducted by the U.S. Centers for Disease Control in 1988 (4) s...

In Silico Serotyping Based on Whole-Genome Sequencing Improves the Accuracy of Shigella Identification

“…Conventional Shigella identification method is labor-intensive, potentially subjective, and not sufficiently accurate. Using molecular profiling, we showed that conventional Shigella serotyping was at best 90% accurate, consistent with a previous report of an upper limit at 91% (17). Similarly, biochemical identification could erroneously assign some Shigella isolates as E. coli.…”

“…Serological differentiation is essential but is laborious, time-consuming, and expensive and can be erroneous. Intra-and interspecies cross-reactivity is common, and commercial antisera are at best 91% accurate (17). Rough strains that do not express O antigen and newly emerged Shigella serotypes without antisera that recognize them are nontypeable, accounting for 6 to 10% of annual Shigella isolates in the United States (8).…”

Clinic-Based Surveillance for Bacterial- And Rotavirus-Associated Diarrhea in Egyptian Children

“…[10][11][12][13] Campylobacter isolates were further speciated using hippurate hydrolysis, 14 and Shigella isolates were serogrouped and serotyped by slide agglutination using commercial antisera (Difco Laboratories, Livonia, MI). 15 In addition, five E. coli-like colonies were picked and tested for the expression of heat-labile enterotoxin (LT) and/ or heat-stable enterotoxin (ST) using a GM1 ELISA. 16,17 Colonies testing positive for LT or ST were further tested for expression of colonization factor (CF) antigens CFA/I, CFA/ II (coli surface antigen [CS] 1, CS2, CS3), CFA/III, CFA/IV (CS4, CS5, CS6), CS7, CS17, PCFO159, and PCFO166 by monoclonal antibody dot blot assay.…”

Identification of Shigella flexneri Subserotype 1c in Rural Egypt

“…Confirmatory identifications were performed with API-20E test kits used according to the instructions of the manufacturer (Bio-Merieux Vitek Inc., Hazelwood, Mo.). Serogroups and serotypes were determined by visual inspection of slide agglutination assays, with commercial antisera used as described by the manufacturer (Difco Laboratories) (10). Briefly, strains were subcultured on tryptic soy agar (Difco) and tested for agglutination on glass slides.…”

“…These serologically atypical strains displayed conflicting agglutination patterns, reacting strongly with serotype 1-specific antisera but also weakly with serotype 4-specific antisera. These equivocal results may reflect the limitations of available commercial antibody reagents to reliably detect the full diversity of serologic variants of S. flexneri (8,10).…”